Present methods of measuring energy deposition spectra in irradiated media are due to H. H. Rossi and his co-workers. The technique involves simulating microscopic absorption sites in an irradiated medium by cavities filled with a gas of the same atomic composition as the cavity wall. Recent observations indicate that subtle and theoretically intractable errors result because of the presence of the density change at the boundary between the cavity and its wall. A spherical proportional counter design that permits the solid-gas interface to be removed from the vicinity of the active region of the detector is described in this paper. Its design, collecting volume geometry, and performance are discussed. The energy deposition spectrum for a broad beam of 4.5 MeV alpha particles is presented.

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